1. Field of the Invention
There is continuing interest in developing new, simpler and more rapid techniques to detect and measure the presence of an analyte in a sample. The analyte may be any of a wide variety of materials, such as drugs, naturally occurring physiological compounds, pollutants, chemicals, contaminants, or the like. In many cases, speed is important for the measurement, particularly with certain physiologically active compounds. In other situations, convenience can be a major consideration.
One convenient and rapid technique which has found wide application is the use of an immunochemical strip, generally comprising a solid rod or film which can be dipped in a sample and subsequently processed to produce a signal based on the amount of analyte in the original sample. There is ample instrumentation to measure a signal, such as light absorption, reflectance or fluorescence produced by a compound bound to a solid surface. Also the immunochemical strip allows for convenient handling, transfers, separations, and the like.
Although convenient, such techniques are highly sensitive to development time, temperature, interfering factors, reagent stability and other conditions which may affect the level of the observed signal.
Accurate detection of an analyte in a sample which is largely insensitive to development time, temperature, interfering factors in the sample, and the like has been achieved (U.S. Ser. Nos. 374,849, filed May 4, 1982, and 399,107, filed July 16, 1982). The method and apparatus involve first and second surfaces, referred to as measurement and calibration surfaces, each involving a signal producing system having at least one catalyst and one substrate, where the systems are substantially the same and involve the same catalyst.
The measurement surface involves the binding of a catalyst conjugate to the surface by means of specific binding pair complex formation associated with the analyte. The amount of catalyst which binds to the surface is related to the amount of analyte in the assay medium.
The calibration surface has a catalyst bound to the surface through the intermediacy of specific binding pair complex formation, where the specific binding pair is different from the binding pair of the measurement surface.
By comparison of the level of signal generating compound at each surface, one can determine whether the amount of analyte is greater or lesser than a predetermined amount, which amount is indicated by the signal generated from the calibration surface.
2. Brief Description of the Prior Art
Patents concerned with various immobilized reagents and different types of test strips include U.S. Pat. Nos. 3,993,451; 4,038,485; 4,046,514; 4,129,417; 4,133,639; and 4,160,008, 4,299,916, and German Offen. No. 2,636,244. Patents disclosing a variety of methods involving separations of bound and unbound antigen include U.S. Pat. Nos. Re. 29,169; 3,949,064; 3,984,533; 3,985,867; 4,020,151; 4,039,652; 4,067,959; 4,108,972; 4,145,406; and 4,168,146.
U.S. Ser. Nos. 374,849, filed May 4, 1982, and 399,107, filed July 16, 1982, are directed to a simultaneous calibration heterogeneous immunoassay.